If you don't want to cut it off all in one go then you need to trim it every 6 weeks. This means you are cutting of the same amount of hair from the ends as it grows. In the mean time use a deep conditioner on it that contains protein a minimum of once a week. (If your hair goes hard you have used it too often.)

Agree with Blueblood if your curl pattern had been affected chances are your hair is beyond salvaging and needs to be trimmed, sorry.

Hydrolysed protein can patch repair the surface and strengthen the cortex but it cannot restore the structural bonds that create curl. Coconut oil is useful for increasing elasticity and reducing porosity. Other proven ingredients include ceramides, 18-MEA and panthenol.

Next time you colour run stand tests in shed plug hole hair, don't use your whole head as a laboratory.